Preprocessing error when trying to concatenate all b-images

Hi MRtrix Community,

I am completely new to MRtrix, as such I have just started the BATMAN tutorial and am struggling with the preprocessing step. When attempting to concatenate the b-images I keep getting this error:

mrcat: [ERROR] unknown format for image “b1000_AP/”
mrcat: [ERROR] error opening image “b1000_AP/”

Any help would be greatly appreciated!